1. Field of the Invention
This invention relates to inlets for capillary gas chromatographs, and more particularly concerns sleeve units for inlet splitters wherein a liquid sample is vaporized into a sample gas and mixed with a carrier gas, and a portion of the gas mixture is split off and delivered to the inlet end of a capillary tube of a gas chromatograph, for splitless sleeves where most of the sample gas reaches the capillary tube, for direct injection and for Septumless Programmable Injectors (SPI) or Programmable Temperature Vaporizing (PTV) Injectors.
2. Description of the Prior Art
Inlet splitters for gas chromatographs are shown and described in Jennings U.S. Pat. No. 4,035,168, issued Jul. 12, 1977, and in an article cited in that patent entitled "Design Considerations and Construction of a Superior Inlet Splitter," by A. J. Ehrler, Victoreen on Chromatography, Issue No. 4 (undated), Victoreen Instrument Division. Both of these documents are incorporated herein by reference, and a copy of each is enclosed.
In the Jennings patent, there is shown in FIGS. 1, 3 and 8 an inlet splitter 10 that is provided with a sleeve unit that comprises a tubular inner liner 66 with a central bore 68 having an inlet opening 72 and an outlet end 76, a rearwardly directed cup baffle 78, a forwardly directed cup baffle 82, a constriction 86 for further turbulent intermixing, and an expansion zone 88 with a terminal portion 90.
The Jennings patent also shows a sleeve unit in FIGS. 6 and 7 which comprises a tubular liner 66 having a bore 68, a rearwardly facing cup baffle 78, a forwardly directed cup baffle 82, dimples 118, and an expansion zone 88 with a terminal portion 90.
Jennings shows another sleeve unit in his FIG. 9 which comprises a tubular liner 166 having a bore 168, a flow restricting baffle 176 which is coupled with a rearwardly facing cup baffle 178, and an expansion zone 142 in which is positioned inlet end 180 of a capillary tube 156 associated with a chromatograph.
In Jennings, as in other splitter units for capillary gas chromatography, the liquid samples are generally introduced into the sleeve unit by a small volume syringe through a rubber septum, for example, Jennings' rubber septum 54.
A problem with the Jennings splitter 10 is that with repeated injections of liquid sample, the self-sealing cap or rubber septum 54 tends to fragment and pieces drop into the bore 68 of the tubular liner 66. While it is a simple matter to remove the sleeve unit and try to rinse out the fragments with some solvent, the Jennings cup design makes it very difficult to rinse clean the sleeve unit. Once fragments collect in the cup, it is virtually impossible to rinse them out.
The Jennings cup splitter sleeve unit has been a standard in the industry for many years. It has many of the features that are generally desired. It is made from glass which is less reactive than metal. The flow path that the carrier gas and sample go through is forced to change directions in the cup or invertor region. This rather abrupt change in direction creates turbulence inside the sleeve unit, and this turbulence is desirable because it promotes mixing of the sample gas with the carrier gas. When the mixed gases finally reach the capillary column, only a small portion of it enters the column and the rest of it exits through the split vent. In this way, the amount or volume gas that is introduced to the column is cut down. In other words, a portion of the mixed gas is split out from the main portion and is directed to the column. Hence, the name splitter sleeve unit.
It is very important that the sample be well mixed with the carrier gas before "splitting" so that a representative portion of the sample reaches the column. For example, if you want one percent (1%) of the sample mixture in the column, you may get one percent of one component and more or less of other components. This non-linearity is undesirable. The cup splitter sleeve unit seems to overcome this problem of non-linearity of the split sample. However, the cup splitter sleeve unit does have a drawback in that it is difficult to clean.